The human endometrium develops new capillaries from existing microvessels, i.e., angiogenesis, which then undergo maturation and remodeling (i.e., investment of microvessels with periendothelial mural cells) into a new vascular network during each menstrual cycle. Improper vascularization of the endometrium may cause implantation failure and infertility. Estrogen and progesterone have pivotal roles in establishing this vascular bed, but their cellular sites and mechanisms of action are incompletely understood. Vascular endothelial growth/permeability factor (VEG/PF), and other angiostimulatory, e.g., angiopoietin-1 (Ang-1), and angioinhibitory, e.g., Ang-2 and thrombospondin-1 (TSP-1), factors interact to control vascular development, remodeling and regression. During the recent SCCPRR project period, we showed that the expression of VEG/PF in glandular epithelial and stromal cells isolated from the endometrium by laser capture microdissection was decreased to low levels by ovariectomy of baboons and increased/restored to normal by estrogen or estrogen and progesterone. Using a cocultivation system, we showed that estrogen in the presence of human endometrial cells stimulated microvascular endothelial cell tube formation. In Study 1 of Project III, we will use the experimental paradigms recently developed in our nonhuman primate baboon model to test the hypothesis that estrogen and/or progesterone regulate the expression of Ang-1, Ang-2, and TSP-1 by glandular epithelial and/or stromal cells and the VEG/PF neuropilin-1 and Ang-1 Tie-2 receptors by vascular endothelial/vascular smooth muscle cells (VSMC) of the endometrium. In Study 2, we will employ a soluble truncated VEG/PF fit-1 receptor (VEG/PF trap) to sequester VEG/PF in vivo in the baboon uterus, to test the hypothesis that VEG/PF mediates the action of estrogen on microvascular permeability, an early step in angiogenesis. In Study 3, a cocultivation system will be used to test the hypothesis that human endometrial VEG/PF mediates estrogen and/or progesterone action on endothelial cell tube formation and Ang-1 mediates estrogen and/or progesterone action on microvascular endothelial cell/VSMC remodeling. Completion of Project III is expected to lead to a critical understanding of the steroid hormone regulation of angiogenesis and vascular remodeling in the human endometrium.